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In situ X-ray diffraction has been used to study the conversion of ∼3000 A thick, evaporated barium fluoride precursor films to YBCO on buffered metal substrates for a range of conversion time, ramp rate, water vapor pressure, oxygen pressure, and temperature. All films were taken from the same continuously processed tape. Critical current densities as high as 1.34 MA/cm 2 have been obtained for a precursor reaction rate of 2.0 A/s. Higher reaction rates (up to 17 A/s) lead to lower critical current densities and incompletely developed YBCO. The reaction rate increases with increasing P H 2 O , increasing T , and decreasing P O 2 . The reaction rate increases linearly with increasing P H 2 O for the range of pressures used here (0.0125–5.0 mTorr). The formation of non-epitaxial YBCO is generally associated with lower T and higher reaction rate, whereas the formation of barium cerate, which results from a reaction of the precursor and the CeO 2 -capped substrate, is generally associated with higher T and lower reaction rate. General trends in the formation of crystalline phases during conversion may serve as a baseline for development of higher rate conversion processing for thicker, higher performance YBCO.

Fabrication of a biaxially textured, strengthened Ni substrate with small alloying additions of W and Fe is reported. The substrates have significantly improved mechanical properties compared to 99.99% Ni and surface characteristics which are similar to that of 99.99% Ni substrates. High quality oxide buffer layers can be deposited on these substrates without the need for any additional surface modification steps. Grain boundary misorientation distributions obtained from the substrate show a predominant fraction of low-angle grain boundaries. A high critical current density, J c , of 1.9 MA/cm 2 at 77 K, self-field is demonstrated on this substrate using a multilayer configuration of YBCO/CeO 2 /YSZ/Y 2 O 3 / Ni–3at.%W–1.7at.%Fe. This translates to a I c /width of 59 A/cm at 77 K and self-field. J c at 0.5 T is reduced by only 21% indicating strongly-linked grain boundaries in the YBCO film on this substrate.

A reel-to-reel tape handler mounted on a four-circle diffractometer is used to provide a characterization by X-ray diffraction of the entire 1 m length of a YBa2Cu3O7/CeO2/YxZr1−xO2/CeO2/Pd/Ni (YBCO/CeO2/YSZ/CeO2/Pd/Ni) tape. Cube-textured Ni was formed by rolling and annealing; epitaxial CeO2/YSZ/CeO2/Pd buffer layers were deposited by reactive sputtering; YBCO was converted ex situ from Y, BaF2, and Cu codeposited by e-beam evaporation. Rocking curve FWHM (mean±standard deviation) for 95 segments of 1 cm length are: YBCO (0 0 5)=6.2±0.5° , YSZ (0 0 2)=10.4±0.4° , and Ni (0 0 2)=7.6±0.3° . φ scan FWHM are: YBCO (1 1 3)=9.6±0.4° , YSZ (1 1 1)=13.0±0.4° , and Ni (1 1 1)=10.6±0.4° . Greater than 95% of the tape at each point is cube textured from Ni to YBCO. The critical current density Jc is 0.36±0.04 MA/cm2 at 77 K and is inversely correlated with the rocking curve FWHM. Calculations suggest that Jc might be increased by a factor of 2.1 by producing a sharper texture and that the uniformity of the texture will support scaling to kilometer lengths.

Transmission electron microscopy was used to study the microstructure of pulsed laser deposited YBa 2 Cu 3 O 7− δ (YBCO) layers on four different biaxially textured Ni-substrates with epitaxial oxide buffer layers. The oxide layer sequence, YBCO/YSZ/CeO 2 /Ni (YSZ signifies yttria-stabilized zirconia) was the same in each sample, but different deposition techniques were used to deposit the buffer layers. The thicknesses of all three oxide layers varied from sample to sample. A columnar sub-grain structure composed of equiaxed sub-grains in the plane of the film was observed in the YBCO layer of each sample. The sub-grain shape and local mosaic spread (∼3°) appeared to be largely insensitive to the surface topography, density, or method of depositing the YSZ layer immediately below. The sub-grain size (0.2–1.2 μm) increased with film thickness (0.2–2.3 μm), but showed no obvious correlation with the microstructure of the underlying YSZ. The measured misorientation angles ( θ ) at individual sub-grain boundaries suggested that a large fraction of the boundaries in the sub-grain boundary network have θ in the range of 2–3°. For most boundaries, the measured θ was below the 5° “threshold” angle for weak link behavior. Thus, a representative picture of the sub-grain boundary network above a single grain of nickel in a film of sub-micron thickness might be a honeycomb shaped arrangement of 2.5° [0 0 1] tilt boundaries spaced 0.25 μm apart and containing dislocations at a spacing of 10 nm. This structure probably has consequences for the structure of grain boundaries in the YBCO that are replicated from the Ni template below. The superposition of the Ni grain boundary network with the grain boundary network due to mosaic spread almost certainly introduces substantial variations of θ along such boundaries on the sub-micron to micron length scale.

Progress made in the fabrication of rolling assisted biaxially textured substrates (RABiTS) and epitaxial deposition or formation of HTS on such substrates is reported. Significant progress has been made in understanding the role of meso-scale defects such as grain boundaries on long-range current flow of HTS conductors made using the RABiTS approach. Both experimental and theoretical calculations suggest that in well-textured samples these commonly present defects do not provide an intrinsic barrier to current flow in long-length conductors. Significant progress has also been made in the reel-to-reel deposition of oxide buffer layers and in the fabrication of long-length superconductors using the ex situ BaF 2 technique. Finally, non-magnetic, mechanically strengthened, biaxially textured metal templates have been fabricated with high quality oxide buffer layers. Epitaxial formation of YBCO on such substrates yields critical current densities over 1 MA/cm 2 at 77 K, 0 T.

A reel-to-reel electron beam evaporation system has been developed to continuously deposit Y–BaF2–Cu precursor for ex situ YBa2Cu3O7−x (YBCO) processed films. The quality of a YBCO film on biaxially textured, oxide buffered, Ni tape strongly depends on the condition of the precursor deposit. For continuous precursor deposition, a uniform cation stoichiometry (i.e., Y:Ba:Cu=1:2:3) over the entire length of precursor film is essential. Rutherford backscattering spectrometry studies indicated that the partial pressure of water vapor during the deposition has a significant effect on cation deposition rates and the oxygen content in the precursor film. The oxygen content of the precursor is increased and the precursor stability upon exposure to air is improved by introduction of water vapor during precursor deposition. High quality precursor films with a thickness of 300 nm have been deposited on lengths of rolling-assisted, biaxially textured substrates in the reel-to-reel electron beam evaporation system. In this paper, long length precursor deposition processing will be discussed. Properties of some post-annealed YBCO films will also be presented.

The electromagnetic connectivity and microstructure of three YBa 2 Cu 3 O 7− δ (YBCO) films grown on biaxially textured substrates were investigated by magneto optic (MO) imaging and scanning electron microscopy (SEM). The films were deposited by pulsed laser deposition (PLD) on yttria-stabilized zirconia (YSZ) and CeO 2 -buffered, biaxially textured Ni tapes. The transport critical current density ( J c ) values of the films were 0.3, 0.6 and 0.7 MA/cm 2 (77 K, 0 T). MO imaging revealed clearly granular electromagnetic behavior in the lowest J c and one of the higher J c samples, but considerably better connectivity in the sample with a J c value of 0.6 MA/cm 2 . High resolution SEM showed a dense and rather featureless microstructure in the YBCO of the most highly electromagnetically connected sample, whereas pores and/or second phase particles cluttered the YBCO layers of the granular samples. Thus, the granular behavior in these samples appears to be caused by pores and second phase particles that locally obstruct the superconducting current in the YBCO layer. Control of these types of defects clearly is important for raising the J c value.

The transport critical current ( I c ) of polycrystalline (Tl 0.5 Pb 0.5 )(Sr 0.8 Ba 0.2 ) 2 Ca 2 Cu 3 O x (Tl1223) and Bi 2 Sr 2 CaCu 2 O x (Bi2212) conductors has been determined for a range of temperature (25–77.3 K) and a range of externally applied magnetic field ( H app = 0–1.5 T). Hysteresis of the I c versus H app behavior has been observed for the Tl1223 conductor and has been interpreted using Bean's critical state model [1]. For the Tl1223 conductor, the remnant critical current measured for H app = 0 after exposure to 1.5 T was found to be independent of temperature. This behavior has been shown to be consistent with the critical state model. No hysteresis of I c versus H app was detectable for the Bi2212 conductor.

Studies have been undertaken using thermal analysis, in conjunction with high-temperature and room temperature X-ray diffraction, fraction, to elucidate phase relationships during thermal processing of thick films of initially phase pure Bi2Sr2CaCu2Oy (2212) on silver substrates in various oxygen-containing atmospheres (0.001 to 100% O2). Exothermic events on cooling at 10°C/min from a partially liquid state vary with oxygen partial pressure and can be grouped into three sets (I–III). Set I is prominent for 0.001% and 0.1% O2 in the range of 740–775°C and is believed to be associated with the crystallization of a Cu-free ∼ Bi5Sr3Ca1 oxide phase. Set II results from the crystallization of 2212; it is observed for p(O2)≥1.0% in the temperature range 800–870°C. Set III appears for 21% and 100% O2 in the temperature range 880–910°C, and its origin is not clear from the results of this study. Subsequent room temperature X-ray diffraction from these samples suggests that in general high oxygen partial pressures (100% O2) tend to favor the formation of Bi2Sr2CuO6 (2201), whereas low oxygen partial pressures (0.001-0.1% O2) lead to the formation of a Cu-free, Bi-Sr-Ca oxide phase. The 2212 phase forms at this cooling rate predominantly for intermediate oxygen partial pressures (7.6–21% O2). High-temperature X-ray diffraction during cooling (2°C/h) from the partially liquid state shows a pronounced dependence of the order of evolution of crystalline 2212 and 2201 phases on p(O2). For an oxygen partial pressure of 1.0% the formation of 2212 precedes that of 2201, whereas for 0.01% O2 2201 crystallizes at a higher temperature than 2212. The implications of these results pertaining to thermal processing of thick 2212 films are discussed.